NOTES  ON  SOME  CRUSTACEANS  FROM  THE  CHEMUNG 

GROUP  OF  NEW  YORK. 


By  JOHN  M.  CLARKE. 


[From  15th  Annual  Report  of  the  State  Geologist.] 


NOTES  ON  SOME  CRUSTACEANS  FROM  THE  CHEMUNG 

GROUP  OF  NEW  YORK. 


By  JOHN  M.  CLARKE. 


72^9 


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d 5 ^y\  ■ • 


Notes  on  Some  Crustaceans  from  the  Chemung  Group  of 

New  York. 


John  M.  Clarke. 


5- 

15 

Q<- 


I.  A Singularly  Ornamented  Phyllocarid  Genus,  Pephricaris. 

By  the  courtesy  of  Professor  A.  B.  Crandall,  of  Alfred  university, 
Alfred,  N.  Y.,  and  the  kindness  of  Mr.  Charles  Butts,  of  the  same  place,  I 
have  been  permitted  to  study  specimens  of  a new  crustacean  allied  to  Eclii- 
noearis^  but  noteworthy  for  the  extravagant  nature  of  its  armature.  Of  these 
specimens,  two  in  number,  the  more  complete  belongs  to  the  museum  of 
Alfred  university  and  is  a sculpture-cast  of  essentially  the  entire  test,  the 
valves  of  the  carajDace  being  expanded  without  distortion  and  the  abdominal 
segments  showing,  in  part,  in  the  posterior  hiatus  of  the  carapace  valves  and 
thence  normally  protruding  behind.  The  second  specimen,  the  property 
of  Mr.  Butts,  is  only  the  echinate  margin  of  one  carapace  valve. 

The  general  aspect  of  the  carapace  is  not  -unlike  that  of  some  species  of 
Ecliinocaris^  yet  it  is  devoid  of  the  curved  sigmoid  carina  which  characterizes 
typical  species  of  that  genus. 

The  carapace  valves  are  broad,  their  margins  curving  rapidly  outward 
for  about  one-half  of  their  length,  slowly  i*ecurv- 
ing  near  the  middle  and  thence  more  rapidly 
receding  to  the  posterior  extremity.  The  expanded 
valves  lie  with  a moderately  broad  anterior  or 
rostral  cleft,  but  there  is  no  evidence  of  a separate 
rostral  plate.  They  are  in  contact  just  back  of  the 
apex  of  this  cleft,  but  for  only  a short  distance,  as 
the  underlying  abdominal  segments  are  partly 
exposed,  a fact  which  may  be  due  either  to  this 
being  the  normal  attitude  of  the  valves,  or  to  casual 
separation  of  them,  or  again  to  a breaking  of  the 
edges  of  the  cast  which  is  not  altogether  clear  at  this 
place.  The  surface  of  each  valve  is  divided  into  two  convexities  by  an  oblique 
depression  beginning  at  the  dorsal  edge  just  back  of  the  middle  and  extend- 
ing backward  \vith  gentle  obliquity.  This  groove  does  not  reach  the  margin 


Figure  1. 

Pephricaris  horripilata,  Chemung 
samLstone,  Alfred,  N.  Y. 


732 


Refokt  of  the  8 fate  GEoLu(usr. 


of  the  valve.  The  anterior  convexity  is  much  the  larger.  Usually,  in  JEchi- 
nocaris.  there  is  a number  of  paired  nodes  and  tubercles  grouped  about  the 
cephalic  extremity  of  the  carapace,  but  in  this  fossil  there  is  only  a single 
[)air,  represented  by  two  deep  pits  situated  close*  upon  the  hinge  and  at  the 
apex  of  the  rostral  cleft.  It  is  possible  that  these  are  remains  of  ocular 
nodes,  but  theii*  depth  suggests  the  probability  of  their  having  been  basal 
attachments  of  the  larger  legs.  Behind  these  nodes  begins  an  ol)lique  and 
strong  ridge,  thickest  and  most  elevated  at  the  hinge,  where  the  anterior 
edges  of  the  ridges  on  the  two  valves  meet.  This  ridge  departs  backward 
into  the  median  groove,  passes  down  its  anterior  slope,  then,  with  a slight 
change  of  angle,  along  the  groove  and  rises  slightly  on  its  opposite  slope, 
terminating  with  the  groove  itself.  The  margin  of  the  carapace  is  some- 
what thickened  and  elevated. 

Nowhere  in  do  w e find  a carapace  structure  like  this,  even 

among  the  species  of  the  Chemung  group.  The  lateral  curved  carina  is  one 
of  the  constant  characters  of  the  genus  and  may  even  be  duplicate  in  later 
species.  The  median  sinus  exists  there,  normally,  only  as  a depression 
betw'een  nodes,  and  no  species  is  so  free  of  cephalic  nodes  as  this. 

As  to  the  abdominal  segments,  Ave  find  that  three,  and  a portion  of  a 
fourth,  protrude  beyond  the  carapace  ; between  the  carapace- vah^es  Ave  make 


Figure  2. 

Pephricaris  horri- 
pilata,  margin  of 
left  valve. 

spines.  These  are  shortest  at  their  commencement  on  the  anterior  margin, 
gradually  increase  in  size  posteriorly,  their  greatest  length  being  reached 
on  the  post-lateral  curve,  and  thence  to  the  posterior  angle  of  the 
carapace  they  liecome  shorter.  The  maximum  length  attained  by  these 
spines  is  not  less  than  one-half  of  the  greatest  diameter  of  a carapace  vah^e. 
That  these  processes  are  spinous  extensions  of  the  chitinous  test  substance, 
and  not  liiindles  of  setje,  or  of  other  nature,  is  shoAvn  by  the  aspect  of  the 
im})i*ints  they  have  left  in  the  matrix,  these  being  sharply  defined 


out  traces  of  tAvo  or  three  others,  estimating  the  entire 
number  at  seven.  The  posterior  segments  are  unusually 
short  and  haA^e  short  spinules  at  their  post-lateral  extremi- 
ties ; there  may,  also,  have  been  such  spinules  elseAvhere  along 
the  posterior  edge  as  in  Echinocaris,  but  such  are  not  seen. 
The  caudal  plate  is  short  and  triangular,  Avith  a short  telson 
and  tAVO  long  curved  cercopods. 

The  fossil  bears  a striking  ornamentation  or  armature. 
The  entire  outer  margins  of  the  carapace  valves  carry  a 
single  roAv  of  broad,  strong,  erect  and  slightly  recurAung 


Clarke — Crustaceans  from  the  Chemung  Group. 


788 


and  clean-edged  throughout  their  extent ; and  again  by  the  presence  of  similar 
but  straighter  and  more  slender  spines  upon  the  final  segment  of  the  abdomen. 
Of  the  latter,  two  pairs  are  visible,  the  penultimate  pairs  appearing  to  be 
somewhat  longer  than  the  ultimate  ; there  are  traces  also  of  a similar  pair  on 
the  antepenultimate  segment. 

This  description  presents  all  the  known  characters  of  this  peculiar 
crustacean.  Its  essential  structure  is  nearest  to  Echinocaris  and  yet  not  in 
harmony  with  that  genus,  and  its  extravagant  decoration  emphasizes  that 
generic  difference.  For  this  reason  the  generic  term  Pephricaris  is  adopted 
for  the  fossil,  and  the  species  may  be  known  as  Pephricaris  horripilata. 

Both  specimens  of  the  species  were  found  in  loose  blocks  of  compact 
Chemung  sandstone  at  Alfred,  N.  Y.  Neither  shows  associated  fossils. 

II.  The  Chemung  Trilobite,  Bronteus  senescens,  Clarke. 

In  the  Report  of  the  New  York  State  Geologist  for  1888,  the  writer 
described  the  trilobite  above  named.*  The  single  specimen  upon  which  the 
description  then  published  was  based,  was  but  a very  imperfect  fragment  of 
a pygidium  and  the  only  justification  for  drawing  attention  to  the  fossil  was 
the  extreme  rarity  of  all  trilobites  in  the  Chemung  faunas.  At  the  date  of 
that  writing  the  presence  in  the  Chemung  of  the  species  Phacops  rana.  Green, 
common  in  the  Hamilton  rocks  beneath,  and  not  of  infrequent  occurrence  in 
the  Ithaca  fauna  immediately  below  the  Chemung  formation,  was  suspected, 
and  had  been  announced.  Later  evidence  has  not  confirmed  this  statement, 
and  we  know  to-day  only  two  described  species  of  trilobites  from  this  fauna ; 
the  Cyphaspis  lcevi%  Hall  (sp.),  the  original  and  only  known  specimen  being 
a cephalon,  and  Bronteus  senescens.  The  presence  of  the  genus  Homalonotus 
is  shown  by  a fragment  from  the  higher  beds  in  Alleghany  county.  Since 
the  description  of  Bronteus  senescens^  founded  on  a specimen  from  the  lower 
Chemung  strata  in  the  town  of  Prattsburgh,  Steuben  county,  additional 
material  has  been  obtained  which  sets  forth  the  characters  of  the  species  in  its 
entirety  and  also  shows  that  from  the  fragment  previously  figured  and  the 
restored  outline  at  that  time  given  to  the  pygidium,  it  might  prove  difficult  to 
recognize  the  species  when  at  its  best.  A restatement  of  the  characters  of  the 
fossil  drawn  from  our  amplified  knowledge  of  it,  will  therefore  serve  to  clearly 
define  the  value  of  this  species. 

* The  Genus  Bronteus  in  the  Chemung  Rocks  of  New  York,  op.  cit..,  Figure  1 ; also  published  in  Forty-sec»^nd  Annual  Report 
Trustees  State  Museum,  pp  403-405. 


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Report  of  the  State  Geologist. 


' Soon  after  the  publication  of  the  article  above  cited,  the  writer  located 
the  horizon  at  which  this  fossil  occurs,  on  Bardeen’s  farm  in  the  northern 
part  of  the  town  of  Prattsburgh,  finding  here  several  nearly  entire  pygidia. 
This  horizon  is  well  characterized  by  the  constant  association  of  this  trilobite 
with  the  Arthrdcantha  deprema ; a species  recently  described  by 

W achsmuth  and  Springer  from  specimens  collected  at  this  locality  where  its 
S2:)inous  plates  are  very  common.  It  is  the  zone  of  Wt  t/nchonella  {Pucjnax) 
pucjivm^  Sow.,  and  is  an  eastward  extension  of  this  zone  from  its  somewhat 
moi'e  prolific  manifestation  at  High  Point,  in  the  town  of  Naples.  More 
recently  two  essentially  entire  specimens  of  the  trilobite  have  been  obtained 
from  higher  strata  of  the  Chemung  group,  near  Avoca,  Steuben  county, 
through  the  agency  of  Mr.  Clifton  J.  Sarle,  both  excellently  preserved  though 
lacking  a few  details,  but  presenting  us  with  a reall}-  striking  exempli- 
fication of  the  late  continuance  of  this  genus. 

Figures  of  these  specimens  are  here  given  and  the  description  of  the 
characters  of  the  species  is  as  follows : 


Figures  3 and  4.  Bronteus  senescens  ; two  nearly  entire  individuals  from  the  Chemung  group, 

near  Avoca,  N.  Y. 

General  Proportions.  The  outline  of  both  of  these  extended 
individuals  is  quite  regularly  ovo-elliptical,  the  shorter  curve  being  at  the 
posterior  extremity.  In  length  the  larger  measures  54  mm.,  the  smaller,  46 
mm.,  AN'hile  the  greatest  width  of  the  animal  is  about  one-half  this  dimension 
in  b(.)th  cases.  The  specimens  have  been  subjected  to  slight,  if  any,  vertical 
compression  though  the  heads  are  some^vhat  askew ; the  lines  of  the  margin 
may,  therefore,  be  regarded  as  normal. 


Clarke — Crustaceans  from  the  Chemung  Group. 


735 


Cephalon.  The  head  is  short  and  subsemilunar  in  outline,  the  posterior 
margin  being  quite  direct.  Its  length  is  slightly  more  than  one-half  its  width. 
The  genal  angles  are  somewhat  produced  into  short  and  broad  spines.  The 
margin  is  elevated,  while  the  border  of  the  head  is  broadly  concave,  rising  on 
its  proximal  limb  to  a genal  ridge.  The  eyes  are  small,  well  back  on  the 
cheeks  and  moderately  elevated,  the  surface  between  the  palpebrum  and  the 
<iorsal  furrows  being  notably  convex.  The  facial  sutures  are  normal. 
The  glabella  is  elongate  and  clavate,  its  width  at  the  anterior  extremity 
where  it  reaches  but  does  not  overhang  the  margin,  being  twice  that  just  in 
front  of  the  occipital  ring.  In  contour  it  is  depressed  convex,  though  its 
elevated  median  portion  attains  greater  elevation  than  any  other  part  of  the 
cephalon.  The  dorsal  furrows  are  deep  and  narrow;  starting  from  the 
posterior  margin  they  approach  each  other  rather  abruptly ; the  curve  changes 
at  the  level  of  the  posterior  part  of  the  eyes  and  thence  forward  the  furrows 
diverge  outward  rather  gradually,  broadly  recurving  near  the  anterior  margin. 
The  lateral  furrows  are  short  but  distinct,  the  first  and  third  pairs  being 
most  clearly  defined,  a median  pair  making  but  a gentle  depression  upon  the 
surface,  while  the  occipital  groove  is  broad  and  shallow. 

The  occipital  ring  is  likewise  broad  and  distinct,  but  its  prolongation  to 
the  cheeks  is  narrower  and  much  more  faint. 

In  one  of  th^  specimens  the  removal  of  the  j)art  of  the  glabella  has 
exposed  a portion  of  an  elongate  liypostome  with  an  oval  central  depression, 
surrounded  by  a narrow  regular  groove  and  bordered  by  a narrow  flattened 
margin. 

Thorax  with  the  normal  number  of  ten  segments.  The  axis  is  very  broad, 
having  fully  one-third  the  entire  width  of  the  thorax,  and  its  margins  curve 
outward,  approaching  each  other  posteriorly.  On  the  axis  the  segments  are 
moderately  broad  and  flat,  distinctly  elevated  along  the  median  line  with 
general  longitudinal  depressions  on  the  lateral  slopes  and  a slight  anterior 
bend  at  the  sides.  On  the  pleurae,  the  segments  are  narrow  and  soon  become 
free  of  each  other,  tapering  rapidly  to  slender,  recurved,  acute  extremities. 

PvGiDiUiVr  semielliptical,  fiabelliform ; length  and  width  about  ecpial. 
Axis  very  short,  extending  for  not  more  than  one-fifth  or  one-sixth  of  the 
plate ; triangular,  elevated  medially  and  with  an  obscure  centra]  lobe  and 
depressed  lateral  slopes.  The  pleura)  are  broad,  flat,  separated  by  sharpl}' 
defined  flat  grooves.  They  broaden  rapidly  outward  and  finally  become 
merged  into  the  grooves  near  the  periphery  of  the  plate,  so  that  the  margin  of 
the  latter  is  smooth.  These  ribs  are  fifteen  in  number;  the  median  ril)  l)eing 


736 


Report  of  the  State  Geologist. 


somewhat  broader  than  the  rest  and,  in  the  larger  specimen,  showing  a 
tendency  to  division  along  its  distal  portion.  The  margin  of  the  pygidiiim  is 
without  evidence  of  spines.  In  general  contour  this  plate  is  broadly  depressed 
within  the  slightly  elevated  periphery,  convex  over  the  central  region  and 
again  sharply  depressed  about  the  axis. 

Orxa:\ientation.  The  entire  test  is  pretty  uniformly  pustulose,  the 
pustules  varying  somewhat  in  size  and  being  coarsest  on  the  glabella  and  the 
ribs  of  the  pygidium.  About  the  enfolded  margins  of  the  cephalon  and 
pygidium  the  surface  is  marked  by  the  usual  incised  inosculating  lines. 

Observations.  This  species  is  noteworthy  not  alone  for  the  rarity  of 'all 
trilobites  at  this  horizon.  It  is,  in  all  probability,  the  latest  representative 
of  the  genus,  making  its  appearance  in  this  later  division  of  Devonian  time, 
subsequent  to  the  first  intrusion  of  Spirifer  disjurictus  and  long  after  the 
only  observed  occurrence  in  this  country  of  Clymenia.  It  appertains  to  a 
fauna  which,  considered  in  its  local  I'elations  and  in  correlation  with  faunas  of 
other  countries,  characterizes  the  final  stages  of  the  Devonian,  and  in  these 
we  have  no  other  record  of  the  occurrence  of  Bronteus.  In  this  late  survivor 
of  the  genus,  therefore,  we  may  expect  to  find  structural  traits  indicative  of, 
or  in  harmony  with  its  late  appearance.  W e observe  that  between  the  earlier 
(upper  Silurian  and  early  Devonian)  and  the  later  Devonian  representatives  of 
this  genus  there  are  contrasts  in  the  form  of  the  glabella,  the  outline  of  the 
pygidium  and  the  nature  of  its  ribs.  Thus,  the  glabella  (or  we  should  rather 
say  the  cranidium,  as  the  distinction  depends  on  the  varying  distance  between 
the  facial  sutures)  is  very  wide  anteriorly,  the  dorsal  furrows  being  highly 
concave  within  the  ocular  nodes  (compare  B.  palifer^  Beyr.,  Lower  Devonian, 
Zittel’s  figure,  Grundzlige  der  Palaeontologie,  p.  473,  fig.  1,279a;  Katzer’s 
figure,  Geologie  von  Bohmen,  p.  1,023,  fig.  498-4;  B.  (ximpanifer,  Beyr., 
lower  Devonian.  Beyrich’s  figure,  Einige  bohmische  Trilobiten,  Plate,  fig.  6 ; 
B.  Partsch%  Barr.,  upper  Silurian,  Katzer’s  copy  of  Barrande’s  figure,  op.  city 
p.  937,  fig.  377-2  ; B.  viator.,  Barr.,  lower  Devonian,  Novak’s  figure  in 
Katzer,  op.  cit.,  p.  1,036,  fig.  548-1 ; B.  acarnas.,  Hall,  Niagara  group.  Twentieth 
Annual  Report  New  York  State  Cab.  of  Natural  History,  PL  II,  fig.  19  ; 
B.  Iwnatu.s.  Billings,  Trenton  limestone.  Geology  of  Canada,  p.  188,  fig.  187, 
and  Clarke’s  figure.  Geological  Survey  of  Minnesota,  Vol.  HI,  Part  2,  p.  725, 
fig.  43).  In  all  of  these  and  numerous  other  recoi*ded  examples  the  feature 
i*ef erred  to  is  strongly  manifested.  If  on  the  other  hand,  Ave  turn  to  species 
of  the  middle  Devonian,  the  nai*i*owing  of  the  glabella  and  the  interval 
between  the  facial  sutures  becomes  evident  (see  B.  -jiahellifer^  Gold  fuss, 


Clarke — Crustaceans  from  the  Chemung  Group. 


737 


System.  Uebersicht,  PL  VI,  fig.  3 ; B,  nieri(lio)iali%  Trom.  and  Grasset, 
Barrois’s  figure,  Calc,  k Polypiers  de  Cabrieres,  Plate  I,  figure  2a  • 
B.  thysanopelti.%  var.  Waldsdimidti,,  v.  Koenen,  Waldsclimidt’s  figure,  Zeitschr. 
d.  d.  Geol.  Gesellsch.,  Vol.  XXXVII,  PI.  XXXVIII,  fig.  2 ; B.  senescens,  etc., 
etc.).  This  feature  appears  to  be  one  which,  irrespective  of  other  variations 
in  structure,  has  gradually  passed  through  the  change  noted,  and  it  is, 
naturally,  to  be  observed  that  lower  Devonian  faunas  embrace  species,  some 
with  the  wide,  some  with  narrower  glabella,  while  thereafter,  the  earlier 
type  of  glabella  has  disappeared. 

With  reference  to  the  characters  of  the  pygidium  in  this  genus  it  may  be 
remarked  that  the  only  really  useful,  tenable  subdivision  of  the  group  is 
founded  upon  the  presence  of  spinules  upon  the  pygidial  margin.  This  is 
Thyanopeltis^  one  of  the  names  introduced  by  Corda  and  designed  by  its 
author  to  include  species  of  this  character;  it  has  proven  to  possess  a definite 
stratigraphic  value.  In  matter  of  outline  there  is  considerable  variation,  from 
the  subsemicircular  shape  in  the  earliest  species  like  B.  lunatm^  Bill.,  of  the 
Trenton,  B.  laticauda^  Wahlenberg,  of  the  lower  Silurian  of  Sweden,  and  B. 
hihernicus,  Portlock,  of  the  Caradoc,  to  the  elongate-elliptical  curve  presented 
by  the  species  of  the  Devonian.  In  this  feature  B.  senescens  is  extreme, 
surpassing  the  elongate,  narrowing  tail-plate  of  B.  Kielcemis^  Gurich,  of  the 
lower  upper  Devonian  (Cuboides  horizon)  of  Poland.  Corda  (Prodrom  einer 
Monographie  der  bohm.  Trilobiten,  pp.  58,  59,  1847),  attempted  a further 
division  of  the  genus  on  the  basis  of  the  simplicity  or  duplication  of  the 
median  rib  of  the  pygidium,  proposing  for  such  species  as  show  a bifurcation, 
the  name  Bicranactis^  and  for  those  in  which  it  is  simple,  Holomeris.  It  has 
long  been  evident,  and  is  shown  in  the  species  in  hand,  that  the  duplication 
of  this  rib  is  of  such  minor  significance  that  it  can  be  regarded  only  as  an 
individual  character  and  we  can  not  safely  infer  values  from  this  trait. 

Barrande  observed  (Systeme  Silurien,  Vol.  I,  p.  840)  that  a division  of 
the  species  of  Bronteus  might  be  founded  upon  the  number  of  ribs  on  the 
pygidium,  which  are  either  six,  seven  or  eight  on  either  side  of  the  median 
rib.  By  far  the  greater  number  of  species  possess  seven  ribs,  while  six  such 
ribs  are  present  only  in  the  earliest  species,  e,  g.^  B.  Iwnatus,  B.  hibernieu.% 
B.  laticauda.  Herein  B.  senescens^  having  seven  ribs,  perpetuates  the  struc- 
ture of  the  normal  representatives  of  the  genus. 

The  definite  time  value  of  the  subgenus  Tliymnopelti^  has  been  set  forth 
by  Barrois,  Kayser,  Freeh  and  other  writers.  The  only  representative  of  this 
division  yet  known  in  American  faunas  is  the  species  B.  tallius^  from  the 


738 


Report  of  the  State  Geologist. 


Tully  limestone  (Cuboides  liorizon)  of  New  York.  Though  the  group  is 
well  represented  in  lower  Devonian  horizons,  there  is  no  record  of  its  per- 
durance  beyond  the  Cuboides  horizon,  and  we  notice  that  in  this  late  represen- 
tative of  Thysanopeltis  the  marginal  spines  are  minute  and  hair-like.  Within 
the  limitations  of  this  group  we  find  the  glabella  passing  through  variations 
in  dimensions  quite  similar  to  those  which  characterize  the  genus  as  a whole. 

Bronteus  senescens  is  devoid  of  marginal  spines  and  reproduces  the  char- 
acters of  the  normal  middle  Devonian  type.  We  look  upon  this  species, 
therefore,  as  distinctly  progressed  in  the  character  of  its  glabella  and  pygi- 
dium  and  as  having  escaped  entanglement  with  the  early  Devonian  divergence 
into  Thysanopeltis ; a survival,  with  appropriate  time  modifications,  of  the 
proper  expression  of  the  genus. 


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